Arboretum's Harmony is a formant-based pitch shifter, corrector, and harmony processor that the company calls a "word processor for vocals." The software offers 9-voice mixing and the ability to make both macro and micro adjustments to audio files through a simple and intuitive graphical user interface. These adjustments are never destructive; you can always return to the original file.

Using the company's proprietary formant-shifting processing, Harmony retains realistic vocal and instrumental sound quality even after transposition (avoiding the "Chipmunks" effect). It also opens up a wonderful world of possibilities for creating fantastic vocal sounds for all kinds of sound-design applications. Not intended for real-time processing, Harmony is an offline arranging tool.

LET'S HARMONIZEHarmony is not an independent application, but a plug-in for Arboretum's HyperEngine, a simple freeware program that allows rudimentary editing of sound files and acts as a manager for several Arboretum plug-ins. HyperEngine can also process sounds from various sources in real time, depending on the capability of the plug-in. A simple panner, lowpass filter, and ring modulator come free with HyperEngine, and demo versions of other plug-ins, including Harmony, are available at the Arboretum Web site.

Harmony 1.0 is designed to process files with single-voice, monophonic melodic material. The mono restriction is absolute: Harmony will not process stereo files. On the other hand, it will happily accept single-channel, polyphonic sound files, with some unpredictable and intriguing results. Although it is billed as a vocal processor, it does a great job on single-line instrumental parts as well. In addition, the program's speech processing - which lets you change inflection, gender, age, and so on - is terrific. HyperEngine's I/O capabilities include support for the Korg 1212 I/O, Digidesign Audiomedia II and III sound cards, and Apple's Sound Manager.

Typically, you begin a Harmony session by loading a sound file into HyperEngine and selecting the region you want to work on. (The program supports both AIFF and SDII formats.) Next, you choose Harmony from HyperEngine's Plug-Ins menu, and the main Harmony window appears with the Notes subwindow (the default subwindow) selected (see Fig. 1).

Along the window's left side are buttons for selecting among the four subwindows (Notes, Mixer, Voices, and Process), as well as the Effect In/Out button. To the right of the buttons, consuming most of the display area, is a graph plotting pitch over time. You create a new plot by pressing the Calc button. Across the top of the graph are the tool and Voice selection buttons.

PICK A TOOLTo change the pitch graph, simply select a segment of the graph, which turns yellow. When you move the mouse over the selected segment, the Selection tool's crosshairs turn into a hand, which lets you transpose the segment up or down. The transposed segment then appears in its new location, while the original turns purple - a thoughtful touch. Equally useful is the "pilot light," a small green dot that appears at the bottom left of each tool button you select.

Use the Pencil tool to draw pitch curves for selected segments. The pitch curve is highlighted in yellow, and the original pitch segment turns purple. If you're not satisfied with the effect, redraw it or hit the Redo button to cancel the last edit. The Reset button lets you return to the original pitch graph and start over.

Use the Resize tool to reduce a segment's frequency deviations around a center, or average, pitch. This tool is useful for editing vibrato on individual notes and compressing or expanding a segment's range.

The Zoom tool, represented by a magnifying-glass icon, is simple to use. Click-dragging a rectangle around an area enlarges the area to fill the display; holding down the Option key and clicking in the display area zooms it back out. The small thumbwheel at the bottom of the display lets you scroll while zoomed in. Unfortunately, the thumbwheel's range is limited to the zoomed-in area; you can't scroll through the entire file while zoomed in to a smaller time base.

The Zoom tool could be more sophisticated, however. For example, the zoom-out function would be more useful if it worked in stages, instead of zipping the user back to the original, prezoom display. Fortunately, a readout at the bottom of the Harmony window helps with pitch and time-position navigation.

The Hand tool, or Scroll cursor, allows X-Y scrolling through the display itself. Yet it suffers from the same operational limitations as the thumbwheel.

TUNING AND LAYERINGNeed to correct some pitches in a file? First, from the Scales popup menu, select a scale to which you want to tune the file. Harmony has presets of standard scales including major, minor, and chromatic scales, as well as 15 "exotic" scales such as BeBop, Diminished, Gypsy, and Hindu. Although details on the exotic scales are not provided, they are interesting and evocative. Scales of arbitrary pitches and frequencies are simple to construct and can be saved for later recall.

To tune a segment, simply highlight it and select the scale, and it's done. Well, almost. In reality, program material often has special requirements that demand custom settings, as I'll discuss shortly.

To add a new line to an existing part, you need to activate a new voice with the Voice Selection buttons. If voice 1 is already in use, click on voice 2 to bring up a new display of the file's original pitch; the previous pitch graph appears in a washed-out green. Then you can edit the new voice with any of the available tools.

Before you can hear new voices, you need to unmute them in the Mixer window (see Fig. 2) because processing occurs only when the mixer channel corresponding to a given voice is unmuted. The original sound file defaults to slider 0, and new voices are assigned to sliders 1 through 8. When you first open the Mixer window, sliders 0 and 1 are unmuted, which lets you quickly compare the original file with your first new voice. You will need to unmute the channels of any additional voices.

The Mixer window is a simple and straightforward display that contains the same controls found on any standard mixer, as well as sliders for adjusting a voice's pitch and formant frequencies in half-step increments up to one octave up or down. Not many parameters in Harmony could use MIDI control, but the Pitch and Formant settings are exceptions.

A LITTLE DAB'LL DO YAThe manual's Quick Start guide doesn't tell the whole story of this intriguing software. As I stated before, certain types of program material require special settings for Harmony to work optimally.

The Voices window (see Fig. 3) lets you change the pitch and formant settings of each voice individually. Two of the controls, Global Formant Shift and Global Pitch Shift, duplicate the Formant and Pitch controls in the Mixer display, but with greater precision (the adjustment range is ñ1 octave in 1-cent increments). Although these controls are labeled "Global" in the Voices window, the documentation refers to them as "Voice Formant Shift" and "Voice Pitch Shift," which more accurately describe their operation.

The Humanize control imposes what Arboretum calls a "realistic warble" on the processed sound. (The warble is based on a model of human vocalization.) At medium settings (on a scale of 0 to 100 percent), the effect is indeed very realistic. I tested this function by stripping the vibrato from a recording of a professional singer and adding new vibrato with the Humanize function. The new vibrato was natural sounding, but it didn't fit the musical context as well as the original. Nevertheless, this feature opens up some serious creative possibilities; its effect on a cool-jazz, muted-trumpet solo was spectacular.

The last item in the Voices display is a checkbox that lets you disable formant shifts on transposition. This option often comes in quite handy; for example, small pitch adjustments sound better without formant shifting.

The Process window (see Fig. 4) features additional global-processing parameters. The Minimum and Maximum Frequency controls determine the frequency range in which the software looks for fundamentals. In practice, Harmony's maximum analysis bandwidth of 55 to 3,998 Hz usually must be reduced, which often makes the difference between a workable pitch analysis and one with undesirable artifacts, such as spikes and dropouts.

The Pitch Variation control adjusts the "capture strength" of the pitch detector. If set to a high number, the pitch detector captures large variations in pitch and represents them in the pitch graph; if set to a low number, the software is less able to track wide-ranging variations in pitch. This parameter smooths out the pitch analysis and is consequently one of Harmony's most important controls. The Pitch Sensitivity control helps the software decide if a frequency is a true fundamental, overtone, or subharmonic.

The Correction Strength parameter pertains to pitch correction: high values eliminate pitch variations more completely; low values leave certain subtle pitch inflections unaffected, resulting in a more natural-sounding performance. The Global Formant Shift and Global Pitch Shift controls vary the formant and pitch of all voices equally, within a range of one octave up or down in 1-cent increments.

GETTING THE PREVIEWHarmony can drag your computer's performance down very quickly as you add more voices and processing. But the plug-in's preview mode, which you select using a checkbox in the Process window, alleviates this problem.

I tested Harmony on two Macs: a 400 MHz blue-and-white Yosemite G3 with 128 MB of RAM and a 300 MHz beige G3 with 128 MB of RAM, both running Mac OS 8.6. On the Yosemite, I layered eight voices and monitored them in preview mode; the beige G3 maxed out at six voices. When writing a file to disk, it's easy to forget to uncheck the preview-mode box, which results in sound-quality loss. A prompt from the program would be helpful here. Another checkbox in the Process window, Process to Mono, causes Harmony to write its output as a mono file (the program creates a stereo file by default).

SUMMING IT UPArboretum's Harmony is a fantastic tool that offers all kinds of creative option for processing vocals or any pitched, monophonic material. Its easy-to-use interface makes sophisticated pitch shifting and harmonization simple and controllable. Its sonic possibilities are stunning, and its sound quality is excellent. I tested Harmony with a 1212 I/O and an Audiomedia III card, as well as with Apple's Sound Manager, with excellent results.

The documentation is in HTML format and mostly straightforward and well written. The Quick Start section gets you up and running with very little pain.

One major drawback is that Harmony often crashes, especially when recalculating a pitch graph after changes to the processing parameters and when closing one project and opening a new one. The crashes occurred on both test machines, and deactivating system extensions or assigning more memory to the program didn't solve this troubling problem. Arboretum said it will address this in a revision.

However, Harmony is a terrific processing tool most synthesists, sound designers, composers, and arrangers won't want to miss.